Horizontal vehicle mounted omnidirectional loop antenna having a shorting stub

ABSTRACT

A horizontal rooftop antenna is adapted to be mounted on rolling stock or a highway truck. It is in the form of an end fed shunttype closed loop radiator tuned to frequencies between 2 and 30 MHz.

Umtd States Patent 1 91 1 11 3,725,940 Siple 1451 Apr. 3, 1973 [54]HORIZONTAL VEHICLE MOUNTED OMNIDIRECTIONAL LOOP ANTENNA [56] ReferencesCited HAVING A SHORTING STUB UNITED STATES PATENTS [75] Inventor: RalphJ. Siple, Idaho Falls, Idaho 2,22l,939 11/1940 Bennett ..343/744 [73]Assignee: The United States of America 88 3,299,428 1/1967 Tessari..343/743 represented by the United States Atomic Energy CommissionPrimary Examiner-Eli Lieberman [22] Filed; 8, 1972 Attorney-Roland A.Anderson 1 pp NW 224,490 57 ABSTRACT 1 A horizontal rooftop antenna isadapted to be [52] 0.8. CI. 343/713, 343/743, 343/748, mounted onrolling stock or a highway truck. It is in 343/882 the form of an endfed shunt-type closed loop radiator [51] Int. Cl. ..H0lq 1/32 tuned tofrequencies between 2 and 30 MHZ [58] Field of Search ..343/71l,-7l3,741, 743, 744,

1 343/748; 882 5 Claims, 4 Drawing Figures 26 28 LINE TUNER 2 ANTENNA1.001

VEHICLE ROOF GROUND PLANE/ HORIZONTAL VEHICLE MOUNTED OMNIDIRECTIONALLOOP ANTENNA HAVING A SHORTING STUB BACKGROUND OF THE INVENTION Thereexists a need for a radiating antenna designed for installation on thetop of a semi-trailer truck having a transmitter. In portions of theradio spectrum, difficulties are encountered in mounting antennae onvehicles because of the vertical height necessary to achieve efficiency.To overcome the difficulties, varioushorizontally polarized antennaehave been tried. It has been determined that inches above the trailerroof is the maximum height allowable to permit the vehicle to pass underbridges, underpasses, etc. An antenna mounted by means of suction cupshas been tried and discarded as impractical. In order to have theantenna sturdily mounted yet avoid the possibility of collisions withoverpasses or the like, a construction using a hinged support has provedto be the most satisfactory. The entire antenna can then be raised orlowered as the road conditions require. For rolling stock, thehorizontal antenna need not be mounted to be raised and lowered.

SUMMARY OF THE INVENTION The present invention comprises a mobilehorizontal rooftop antenna which may be used on highway vehicles orrolling stock. It has been found that an antenna .in the form of ahorizontally mounted stainless steel a line tuning network for anecessary impedance match to a transmitter. The antenna structure can beeither rigidly mounted or made to be retractile.

It is an object of this invention to provide an improved mobile antennafor horizontal mounting on a vehicle roof. It is a further object ofthis invention to provide an improved retractile roof-mounted antennacontrolled remotely by air pressure. It is also an object of the presentinvention to provide an improved radiating antenna for a mobiletransmitter.

BRIEF DESCRIPTION OF THE DRAWINGS DESCRIPTION OF THE PREFERREDEMBODIMENT Referring now to the drawings, there is shown in FIG.

1 an embodiment of the present invention to be mounted on a mobilevehicle. A horizontal metal section of the vehicle roof indicated at 10,serves as an electrical ground plane. The antenna, 12, is shaped in thefonn of a rectangle and is supported above the ground plane, 10. Acoaxial cable, 14, has the inner conductor, 16, connected to theantenna, 12. The outer shield, 18, is fastened to the metal surface, 10,with a terminal conductor. The coaxial cable, 14, will vary from 20 to30 feet in length depending on the installation.

A line tuning network, 20, having a variable capacitor, 22, and variableinductor, 24, is connected to the coaxial cable, 14, and to atransmitter, 26, by means of a lead-in line in the form of coaxialcable, 28. An RF signal is fed from the transmitter, 26, into thevariable inductor, 24, which varies from 0-10 microhenries, through thevariable capacitor, 22, which varies between 12 and 202 micro microfarads and through the coaxial cable, 14, to the antenna feedpoint, 30.The gain of the antenna is approximately 8 db.

The antenna structure itself may be made from three-eighths inchstainless steel or copper tubing. As

shown in FIG. 2, the antenna loop can be made up'of two long sides,designated A, and two shorter sides, B and C. A stainless steel stub, D,is attached at a distance, E, from the first side of the loop andparallel to it. A shorting stub, F, connected at a distance, G,

from the feedpoint, 30, joins the stub to the first side. An antennaloop design which performs very well has distance E 5 in.

distance G 10 in.

In the embodiment of FIG. 3, a polyvinyl chloride plastic pipesupporting structure, 32, for the antenna, 12, is depicted. The plasticsupporting structure, 32, has a series of legs, 34, with a crossbar, 36,joining the legs in pairs as shown. The legs, 34, are hinged, 38, at thebottom to the vehicle roof so that the entire antenna may be retracted.A chain, 40, may be used to connect adjacent vcrossbar-s, 36. The hingedsupporting structure, 32, may be raised and lowered by means of ahydraulic cylinder, 42, as shown in FIG. 4. The cylinder, 42, may bemounted on top of the vehicle along with the antenna and supportingstructure. Air can be supplied from the vehicle air supply that is usedfor the vehicles air brakes. The antenna then mayv be raised or loweredby remote control at the drivers discretion.

It has been found that an antenna positioned a distance of 15 inchesabove the vehicle reflector surface provides the best performance. Ithas also been' found that the position of the shorting stub at about 10inches from the feedpoint provides the best radiation of the transmittersignal.

The same configuration described above has been used on rolling stockwith excellent results. On a railroad car, however, the supportingstructure need not a first end of said loop being the feedpoint andconnected to receive a transmitter signal through an inner conductor ofa coaxial cable,

an outer conductor of the coaxial cable being connected to the vehicleroof which constitutes a reflecting ground plane,

a second end of said loop having a conductive stub connected theretospaced parallel to and at a short distance from the first loop side,

a conductive shorting stub positioned at substantially right angles toand joiningthe first side and the conductive stub at a distance from thefeedpoint serving to close the loop,

and an insulating supporting structure attached to the vehicle roof andto the antenna loop in the vicinity of the four corners of the loop,

the supporting structure holding the antenna loop in a horizontalposition at a distance above the vehicle roof.

2. The radiating antenna structure of claim 1 wherein the loop is madeof stainless steel tubing and the supporting structure is made ofpolyvinyl chloride tubing.

3. The radiating antenna structure of claim 2 wherein the supportingstructure is hinged to the top of the vehicle so that the antennastructure may be raised and lowered.

4. The radiating antenna structure of claim 3 wherein a hydrauliccylinder having a remote control operates to raise and lower thesupporting structure.

5. The radiating antenna structure of claim 1 wherein the loop issupported at a distance of about 15 inches above the vehicle roof. I

1. An end fed shunt-type radiating antenna adapted to be mounted on avehicle roof comprising: a continuous generally rectangular open endedconductive loop, a first end of said loop being the feedpoint andconnected to receive a transmitter signal through an inner conductor ofa coaxial cable, an outer conductor of the coaxial cable being connectedto the vehicle roof which constitutes a reflecting ground plane, asecond end of said loop having a conductive stub connected theretospaced parallel to and at a short distance from the first loop side, aconductive shorting stub positioned at substantially right angles to andjoining the first side and the conductive stub at a distance from thefeedpoint serving to close the loop, and an insulating supportingstructure attached to the vehicle roof and to the antenna loop in thevicinity of the four corners of the loop, the supporting structureholding the antenna loop in a horizontal position at a distance abovethe vehicle roof.
 2. The radiating antenna structure of claim 1 whereinthe loop is made of stainless steel tubing and the supporting structureis made of polyvinyl chloride tubing.
 3. The radiating antenna structureof claim 2 wherein the supporting structure is hinged to the top of thevehicle so that the antenna structure may be raised and lowered.
 4. Theradiating antenna structure of claim 3 wherein a hydraulic cylinderHaving a remote control operates to raise and lower the supportingstructure.
 5. The radiating antenna structure of claim 1 wherein theloop is supported at a distance of about 15 inches above the vehicleroof.